One type transmission which has two concentric input shafts and two clutches are those called power shift transmissions, wherein one clutch is engages in all even gear speeds and the other clutch is engaged in all uneven gear speeds. When shifting from one gear speed to the next gear speed this next gear speed is pre-selected and the actual shifting is initiated by releasing the presently engaged clutch and engaging the presently disengaged clutch.
Usually power shift transmission of this type have hydraulically operated multiple wet plate clutches. Pressure from a hydraulic pump keeps the clutches engaged one at the time and the pressure is redirected from one clutch to the other when shifting takes place. When the engine driving the transmission is not running then the clutches are disengaged. During driving one of the clutches is always biased by the hydraulic pressure from the pump to the engaged position which means that some engine power from the engine driving the transmission is consumed by the hydraulic pump thereby decreasing the over-all efficiency of the vehicle drive line compared with a drive line using dry plate friction clutches.
Problems to mechanically alternately engage and disengage two dry plate friction clutches running at different rotational speeds as in the case in a power shift transmission in which one input shaft is driving in all uneven gear speeds and the other in all even gear speeds have, however, so far resulted in that only hydraulically operated multiple wet plate clutches have been used in combination with power shift transmissions.
The purpose of the present invention is to achieve an arrangement as described by way of introduction which makes it possible to use two dry plate friction clutches in combination with a transmission having two input shafts journalled concentric with one another, e.g. a power shift transmission or a hybrid engine transmission.
This is achieved according to the present invention by virtue of an arrangement having a first and a second release bearing one of which co-operates with the first friction clutch and the other one with the second clutch, and a mechanism arranged to apply an axial force to said first and second release bearings in order to disengage the clutches, at least one of said first and second release bearings being arranged to transmit an axial force via a first force transmitting mechanism to a third release bearing extending through a rotating element connected to the second clutch.
By means of the arrangement according to the invention, clutches can be used which have springs, or similar devices, to keep the clutches engaged during driving, thereby eliminating the need for a hydraulic pump applying a hydraulic pressure to keep hydraulic clutches engaged during all driving condition so that the over-all efficiency of the vehicle drive line is increased.